A percussion drilling apparatus can have a drill chuck driven rotatably by a drill spindle, which has an axial passage through which the percussion effect is communicated to a drill held between central movable chuck jaws by a ram member movable axially in and traversing the hollow drill spindle.
A coupling member can be provided for coupling of the drill chuck with the drill spindle, the coupling member being adjacent to or between the drill spindle and the body of the drill chuck.
The coupling member can be axially fixed, but rotatable, and provided with a coupling sleeve surrounding it, securing it, and shiftable to different angular positions about the chuck axis, for example a position in which the coupling member is held firmly in the coupling cavities of the drill spindle, and a further one in which the drill chuck can be removed from the drill spindle.
A drill chuck of this type is known in the art in which drill chuck axial free play is not allowed, which means, that the coupling cavities holding the coupling member in the drill spindle and in the chuck body have the same dimensions in the axial direction as the coupling member, so that the coupling member is held in the coupling cavities in a fixed position axially without axial play during drilling.
Furthermore the coupling sleeve, with the aid of a setscrew which can extend radially of the coupling sleeve, is held against the chuck body, but a comparatively high clamping force is required, because the coupling sleeve contains the guide cavities for the retaining screws for the drill chuck and therefore in operation at no time can rotation of the chuck body be allowed.
However, while no axial play at the chuck with respect to the spindle is desired for rotational drilling, for percussion drilling it is desirable that the drill chuck have some axial displacement play with respect to the drill spindle, in order to prevent the drill chuck with its mass from taking part in the percussion motion which might reduce the percussion effect and its corresponding drilling efficiency. It is also desirable to avoid the use of setscrews and the like which may slip during the drilling operation.